The study, published this week in the Proceedings of the National Academy of Science, analysed the Thwaites Glacier, which is one of West Antarctica's largest, most rapidly evolving and potentially unstable contributors to global sea level rise.

The West Antarctic Ice Sheet (WAIS) lies on top of the vast, hidden West Antarctic Rift System where crustal expansion processes occur deep beneath the ice, and is losing ice faster than any other part of Antarctica.

Although strong evidence has been found previously for the movement of magma and volcanism beneath the ice sheet, limitations in the available data have made it difficult to accurately judge what impact geothermal activity was having on the melting ice.

Now, geophysicist Dr Dustin Schroeder from the University of Texas, and colleagues, are filling in the blanks.

They have used new methods to get the most realistic picture to date of 'geothermal flux' and the pattern of the meltwater, which is carried downstream in large channels beneath the glacier.

"Geothermal flux is the heat that flows from the Earth beneath an ice sheet into the bottom of the ice," Schroeder explains.

"So, if part of an ice sheet is located in a region of high geothermal flux (for example in a region with thin crust or nearby volcanism due to rifting) then it will lead to more melting at the bottom of the ice sheet than if that that ice sheet was located in a region with lower geothermal flux."

State of flux

The researchers found that the Thwaites Glacier catchment experiences variable levels of flux, with the highest levels found the western-most tributary near the ice-covered, dormant Mount Takahe volcano.

Other high flux areas across the glacier catchment are located in areas adjacent to topographical features that are thought to have volcanic origins.

"The nearby volcanoes are an expression of the crustal thinning, magma migration, and volcanism associated with the West Antarctic Rift System," Shroeder says. "The pattern of melting and geothermal flux we observed is also an expression of those same associated processes."

Realistic picture

Schroeder says there have been several recent papers suggesting the melting of the Thwaites Glacier could spread to the rest of the WAIS over the next hundreds to thousands of years.

"When ice sheet modellers try to simulate that process so that they can provide better estimates of the rate of sea level rise, one of the key inputs they need for their models is geothermal flux," he says.

"Before our paper, models tended to just assume a uniform geothermal flux value beneath the glacier because it was the best you could do with the observations available (even though the presence of nearby volcanoes and other geologic evidence suggested it was probably very non-uniform).

In their study, Schroeder and colleagues combined airborne radar data with a subglacial water routing model.

"Our results provide an observation-based set of geologically realistic geothermal flux values that modellers can use to make much more realistic simulations of the future behaviour and sea level contribution of Thwaites Glacier," says Schroeder.